So the drilling industry insisted there was no link at all between fracking and earthquakes, but finally had to admit that injecting fracking wastewater can trigger earthquakes. Now it looks like the actual fracking can trigger earthquakes, after all. Maybe we should put the onus on businesses to prove the safety of what they’re doing first? Nah, that would be un-American!

Drawing on scientific research and reports by government agencies, Smart News and Smithsonian‘sSurprising Science blog have written that, as the National Research Council puts it, “there is no evidence to suggest that hydraulic fracturing itself is the cause of the increased rate of earthquake.” The known link between fracking and earthquakes has been to do with the waste disposal process, not the fracking itself: Inappropriate disposal of waste water used during the fracking process has triggered induced earthquakes.

Earthquake monitoring equipment in northern British Columbia, Canada, says the report, recorded 216 small earthquakes clustered in a small area around an ongoing fracking project in the northern end of the province. Of those earthquakes, 19 of them were rated between 2 and 3 on the Richter magnitude scale. Only one of them was strong enough to be felt at the surface. By comparison, in the past week alone, Southern California experienced 333 earthquakes, with 29 of those having magnitudes from 2.0 to 3.9.

Focusing in on a subset of the earthquakes, the report says,

Eighteen [local] magnitude 1.9 to 3.0 events were selected from dense array microseismic plots. These events were selected because they were located adjacent to hydraulic fracturing stages and could be connected to a single stage fluid injection with some confidence. Evidence strongly suggests that all events were triggered by fluid injection at adjacent stages.

They found that eight of those earthquakes happened while the fracking was ongoing and that all eighteen happened within 24 hours of the fracking injections. The fracking-induced earthquakes happened when the fluid injection caused pre-existing faults within the Earth to slip. The strength of the earthquakes got bigger or smaller the closer or further the fracking was from the fault.

This isn’t the first time a link has been seen between fracking and earthquakes, but the pool of observations remains extremely limited—the report cites other known instances in England and inOklahoma.